In recent years, a multilevel wiring technology has been used to connect wires formed in different layers in order to deal with scaling down of semiconductor devices. As a related-art example of the multilevel wiring technology, a structure can be given which includes a first wiring layer provided on a first insulating layer, an interlayer dielectric which covers the first wiring layer and has a contact hole over the wiring layer, and a second wiring layer provided over the contact hole. In this case, a contact layer (conductive layer) is provided in the contact hole to electrically connect the first wiring layer and the second wiring layer. Copper may be used as the conductive material for the contact layer. Copper has an advantage in that an RC delay can be reduced so that the operation speed can be increased. On the other hand, since copper is a material which is easily diffused into an insulating layer such as an interlayer dielectric, a barrier layer for preventing diffusion may be formed on copper when forming a wire using copper. A silicon nitride film may be used as the material for the barrier layer. However, since the silicon nitride film has a high dielectric constant, a signal delay may occur even if diffusion of copper is prevented. As another material used for the barrier layer, a polycarbosilane film obtained by curing a polycarbosilane compound can be given (see U.S. Pat. No. 5,602,060). The polycarbosilane film disclosed in U.S. Pat. No. 5,602,060 film-forming composition to a substrate and heating the applied composition in an oxidizing atmosphere.